This invention relates generally to video display systems and specifically to a technique for enhancing the viewability of an interlaced video line scanning system.
In a conventional 525 line television signal scanning system, two successive fields are scanned, each comprising 2621/2 horizontal lines that are interlaced with each other. The resultant display, produces a visible line structure since each line is scanned only once in every two fields and therefore is black one-half of the time in every frame interval (=1/29.97 sec). Large area flicker is not normally visible however because of the nominal 60 Hz vertical repetition rate. Techniques have been considered in the prior art for overcoming the visible line structure referred to as "static" raster. This line structure is exacerbated in larger viewing screen sizes, and in large screen projection television systems, is often objectionable. Some systems contemplate double scanning, that is repeating a line to effectively create "fill-in" lines to take the place of the blank (black) lines in successive fields. While the field structure is still interlaced with respect to the real video lines, the actual number of lines scanned in each field is doubled with a corresponding improvement in the video display.
The present invention interpolates between the real lines of video information to develop interpolated lines of video that are based upon the real lines. In the simplest environment the interpolated line is one-half the sum of the immediately adjacent real lines, i.e. those on either side of the interpolated line. The present invention further adds peaking or enhancement to emphasize vertical transitions between successive lines of video in the signal. In the preferred implementation of the invention the video information is in a pix 1 format with the pixels being sampled at four times the color subcarrier frequency (4 fc). Corresponding samples from the real lines are processed to develop the interpolated lines of the video and vertical enhancement is performed on real lines only and in a symmetrical manner.